**1. Introduction**

Over the last decades, changes in forest composition from primeval stages and the rarefaction of certain tree species have raised several concerns for biodiversity conservation [1, 2]. For example, the widespread mortality of ash trees caused by the alien invasive Emerald ash borer (*Agrilus planipennis* Fairmaire), recently introduced in North America, could threaten 43 native arthropod species feeding or breeding only in ash trees [3]. Indeed, exotic insect pests and pathogens may lead to tree species shifts and be a driving force behind important changes in ecosystem processes [4]. This already occurred in western North America where the exotic white pine blister rust, *Cronartium ribicola* J.C. Fisch., introduced at the beginning of the twentieth century, affects seven of the eight white pines (subgenus *Strobus*) [5]. For instance, the whitebark pine (*Pinus albicaulis* Engelmann) has been extirpated locally because of the combined actions of the white pine blister rust, an indigenous insect, and fire suppression policies [6]. These authors consider the whitebark

pine as a foundation species because it provides locally stable conditions needed by several co-occurring species. Its loss thus alters several ecosystem processes such as forest productivity and hydrology [6]. According to Tomback and Achuff [5], without active management, many pine-associated communities may disappear and their loss would result in severe impacts to biodiversity and other ecosystem services. They recommend using timely proactive restoration programmes to avoid or at least mitigate losses in pine ecosystems.

In eastern North America, the eastern white pine (*Pinus strobus* L.) was also much more prevalent in pre-settlement forests than it is today [7–9]. Eastern white pine is the tallest tree in eastern North America and ecologically typifies the northern forests of eastern United States [10]. This noble tree species has been important for economic, social, and cultural reasons [11]. As western white pines, it has been also severely impacted by the exotic white pine blister rust, *Cronartium ribicola* J.C. Fisch [12]. Moreover, fire suppression policies have altered the natural dynamics of eastern white pine stands by allowing shade-tolerant species, such as balsam fir (*Abies balsamea* L.), to outcompete pine seedlings [8, 10, 13–15]. Finally, selective logging of mature eastern white pines during the eighteenth and nineteenth centuries has reduced seed tree density and, thus, its regeneration potential [16, 17].

Historically, eastern white pine regeneration was favoured by surface fires, which improve seedbed quality, increase light availability, and reduce competition from saplings of other shade-tolerant tree species [7, 14, 18]. Mature eastern white pines survive most surface fires due to their thick bark [19], branch-free lower trunks, and deep roots [20]. Their needles have a low content of resin and thus are not highly flammable [21]. Eastern white pine reaches the northern limit of its range in the southern part of eastern Canada, where most ignitions are rapidly suppressed for safety reasons. Other than fire, the natural regeneration dynamics of eastern white pine in old stands is still poorly understood, mainly at the northern limit of its range [11]. Recent studies have recognized the importance of gap dynamics, which is closely related to understory light for seedlings [22, 23]. Uprety et al. [11] concluded that management strategies should be different near the northern range limits because site conditions and disturbances have different effects than in the centre of a species' range. Regenerating eastern white pine thus remains an important challenge and researchers still test methods to reduce the effect of competing vegetation [24]. However, this mainly involves using herbicides [24] or thinning [25], approaches not compatible with the mandate of national parks.

The *Canada National Parks Act* requires maintaining or restoring the ecological integrity of the parks through the protection of natural resources and ecological processes. Ecological integrity is defined as 'a condition that is determined to be characteristic of its natural region and likely to persist, including abiotic components and the composition and abundance of native species and biological communities, rates of change and supporting processes' [26]. Because several parks have been established in areas previously disturbed by logging, Parks Canada often needs to develop management approaches to restore these ecosystems to make them sustainable for future. The objective of restoring the ecological integrity of eastern white pine forest ecosystems to pre-settlement conditions, or at least within their historic range of variability [27, 28], might be achieved by using prescribed burning as a management approach [29, 30]. In the context of a national park, prescribed burning represents a tool for reintroducing a natural ecological process. Prescribed burning has been shown to promote regeneration of several fire-favoured pine species, such as *P. ponderosa*, *P. pungens*, and *P. rigida* [31–34], but its efficacy remains to be demonstrated in eastern white pine forests.

In La Mauricie National Park of Canada, eastern white pine proportion was estimated at 5–12% in pre-settlement forests but now represents only 0.5% of the current forest composition. Meanwhile, balsam fir has increased from 13.1 to 31.8% [35–37].

**41**

**Figure 1.**

*Prescribed Burning to Restore Eastern White Pine Forests of La Mauricie National Park…*

Between 1991 and 2005, a total of 10 Eastern white pine stands have been treated with prescribed burning in La Mauricie National Park of Canada. The objectives of prescribed burning are to generate ecological conditions for increasing eastern white pine seedling density (short-term objective) to bring saplings density up to 100/ha (midterm objective) in order to increase the cover of eastern white pine-dominated stands to 3–4% (long-term objective) in the future forested area of the park [15]. As the number of published studies addressing the ecological effectiveness of management practices in protected areas is limited [38], this restoration programme represents a unique opportunity to evaluate the effects of prescribed burning, as a sustainable management practice for a national park. The objective of this study was to determine if prescribed burning reduces competition and favours eastern white pine regeneration. We hypothesized that prescribed burning would kill most balsam fir competing saplings, thus reducing competition for light and promoting eastern white pine regeneration.

The study was carried out in La Mauricie National Park of Canada (**Figure 1**), which is located in Quebec, Canada. The park was established in 1977 and covers

The altitude of the 16 selected stands ranged between 217 and 341 m and their slope

Prescribed burning was used in stands where eastern white pine density was >15 trees/ha, the slope <50%, and balsam fir saplings dominated the understory. In these sites, eastern white pine seedling and sapling densities were considered too

*Old white pine stand along the Wapizagonke lake in La Mauricie National Park of Canada.*

typical Laurentian Mountains landscape moulded with hills and lakes. Annual precipitations vary between 900 and 1400 mm and annual mean temperatures vary between 2.5 and 5.0°C [39]. Seven stands treated with prescribed burning between 1995 and 2005, and nine unburned stands, were selected over an area of 40 km<sup>2</sup>

. It belongs to the sugar maple-yellow birch bioclimatic domain and is a

.

*DOI: http://dx.doi.org/10.5772/intechopen.86224*

**2. Materials and methods**

varied between 1 and 47% (**Table 1**).

536 km2

**2.1 Study area, stand selection, and burn treatment**

*Prescribed Burning to Restore Eastern White Pine Forests of La Mauricie National Park… DOI: http://dx.doi.org/10.5772/intechopen.86224*

Between 1991 and 2005, a total of 10 Eastern white pine stands have been treated with prescribed burning in La Mauricie National Park of Canada. The objectives of prescribed burning are to generate ecological conditions for increasing eastern white pine seedling density (short-term objective) to bring saplings density up to 100/ha (midterm objective) in order to increase the cover of eastern white pine-dominated stands to 3–4% (long-term objective) in the future forested area of the park [15]. As the number of published studies addressing the ecological effectiveness of management practices in protected areas is limited [38], this restoration programme represents a unique opportunity to evaluate the effects of prescribed burning, as a sustainable management practice for a national park. The objective of this study was to determine if prescribed burning reduces competition and favours eastern white pine regeneration. We hypothesized that prescribed burning would kill most balsam fir competing saplings, thus reducing competition for light and promoting eastern white pine regeneration.
